Poly(amino acids) such as poly(aspartic acid) are useful as cleaning and detergent additives; fertilizer and pesticide additives; personal care product additives; dispersants; and water treatment application and oil production operation additives. For example, European Application Number 454126 A, discloses the use of poly(amino acids) as builders in detergent formulations.
Poly(amino acids) have been synthesized by several different known methods. One known method for synthesizing poly(amino acids) consists of first forming poly(anhydroamino acid) by thermally condensing amino acids and then hydrolyzing the resulting poly(anhydroamino acid) to form poly(amino acid) as disclosed in U.S. Pat. No. 5,057,597. However, poly(aspartic acid) produced by the process of U.S. Pat. No. 5,057,597 is limited to a molecular weight less than 5,000 as measured by aqueous gel permeation chromatography (GPC) relative to a standard of 4500 molecular weight poly(acrylic acid).
Another thermal polycondensation reaction of amino acids is disclosed by Fox, et al., in a publication entitled "Thermal Polycondensation of Alpha-Amino Acids," Analytical Methods of Protein Chemistry, pp. 127-154, Permagon Press, Oxford 1966. Fox discloses a process where phosphoric acid, orthophosphoric acid, or polyphosphoric acid, used as a catalyst, is heated with one or more amino acids at 70.degree. C. to about 210.degree. C. to form poly(anhydroamino acid). Fox et al., reports that the phosphoric acid catalyst increases the reaction yield and molecular weight of the poly(anhydroamino acid).
There are several problems associated with the above mentioned processes for making poly(anhydroamino acid). The process to make poly(anhydroamino acid) using phosphoric acid and one or more amino acids presents difficult processing problems because the mixture of phosphoric acid and amino acid becomes a viscous molten paste upon heating. At the completion of the reaction, the solid product formed may consist of hard, large chunks of solid product. These hard, large chunks may be nonuniform in composition. For example the inner part of the hard, large chunks may contain unreacted amino acid due to less heat being transferred to the inner part. Additionally, the solid product may be caked to the walls of the reaction vessel. Because of these processing difficulties, the resulting solid product may need to be dissolved in solvent or pulverized to recover the poly(anhydroamino acid). The use of solvents creates additional problems, for example, solvent waste is generated which must be disposed of or recycled.
Consequently, it is an aim of the present invention to develop a process for manufacturing amino acid polymers using conventional processing equipment.
It is a further aim of the present invention to provide a continuous process for preparing amino acid polymers.
It is another aim of this invention to provide a relatively simple process for the manufacture of amino acid polymers which requires minimal or no solvent.
It is another aim of this invention to produce amino acid polymers having molecular weights up to 60,000.
It is another aim of this invention to produce amino acid polymers which can be used as: cleaning and detergent additives; fertilizer and pesticide additives; personal care product additives; dispersants for inorganic particulates, aqueous emulsions, and drilling muds; and water treatment and oil production operation additives as corrosion and scale inhibitors.
As used herein, "amino acid polymer" refers to polymeric materials which contain only succinimide moieties in the polymer chain, or contain succinimide and non-succinimide moieties in the polymer chain, and include polymers resulting from completely or partially hydrolyzing the amino acid polymer with an acid or base.